1. Field of the Invention
The present invention relates a device for producing thread-stitched book blocks from a stack of signatures, wherein the signatures are arranged flat one on top of the other and are stitched together by stitched seams formed at right angles to the folds by a double-stranded binding thread that passes through the folds of the signatures from the outside to the inside, runs along the inside edge of the folds, and passes through the folds from the inside to the outside. For each of the stitched seams is provided a first stitching needle that inserts the binding thread through a fold of a signature from the outside and a second stitching needle that draws the binding thread through the fold of this signature from the inside. Means are provided for carrying the binding thread along the inside edge of the fold from the first stitching needle to the second stitching needle, also referred to as a hooked needle. A punch needle, which passes through the fold from the inside edge to form a punched hole, is arranged opposite the first and second stitching needles, each of which forms a stitched seam.
2. Description of the Related Art
A device of the type described above is described in detail, e.g., in the book, “Polygraphische Technik” (“Polygraphic Technology”), VEB Fachbuchverlag, Leipzig, Germany 1978, 1st Edition, EP 0 295 220 A and EP 0 832 758 A2.
These thread-stitching devices use stitching needles and punch needles whose tip consists of a conical section attached to a cylindrical shaft. The conical tip of the needle and the shaft that follows it form circular holes when they pierce the fold. After the stitching operation, a binding thread runs through the holes and holds the signatures together in a book block. The spine of the bound book block is then glued to produce greater spine strength. The glue is applied with slight hang-out of the spine between pressing jaws, so that pressure is produced on the peripheries of the holes through which the binding thread passes. However, this pressure is not sufficient to close completely the holes that are present, so that the glue supplied to the spine of the book block can penetrate the holes and can emerge at the inside edge of a fold. The appearance of the glue at the inside edges of the fold detracts from the quality of the book block.
A wedge-shaped tip of a punch needle is also known and is used for the purpose of producing a squeezable hole. The use of this punch needle leads to the corners of the resulting rectangular holes being torn out.